Method for preparing mixed alkyl esters of phosphoric acid



Patented May 19, 1953 UNITED STATES PATENT OFFICE METHOD FOR PREPARINGMIXED ALKYL ESTERS 0F PHOSPHORIC ACID Kent 0. Brannock, Kingsport,Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application January 26, 1951,Serial No. 208,076

8 Claims. (61.260-461) This invention relates to the preparation ofneutral esters of phosphoric acid in which the However, the methoddescribed in the prior-art for replacing one or two or more of the alkylgroups of a trialkyl phosphate with other alkyl groups is throughalcoholysis. For instance, by the alcoholysis of triethyl phosphate withbutyl alcohol, ethyl dibutyl phosphate or dibutyl ethyl phosphate may beobtained. This method, however, is accompaniedby the'simultaneousformation or substantial quantities of mixed alkyl ethers and alkylphosphoric acids, resulting in very low yields of the describedphosphate-esters.

One object of my invention is to provide a method for replacing thealkylgroups of a tr ialkyl phosphate with other alkyl groups by a methodgiving a substantially better yield than has been :previouslyobtained.Another obj ect of my invention is :toreplace the valkyl groups of atrialkyl phosphate with the alkyl groups of an alkyl chlorosulfinate or.chloroformate. Other objects of .my invention will appear herein.

placement depends in part on the relativequantities of the two reactantswhich are present in the reaction mass. If desired, the alkyl phosphateemployed as thestarting material may be a mixed alkyl ester, in whichcase the product may contain amixture of various alkyls. In the reactiondescribed the use of equimolar quantities of the trialkyl phosphate andthe .alkyl chlorosulfinate or chloroformate gives primarily a product inwhich only one of the .alkyls of the trialkyl phosphate is replaced. Ifthe relative quantityof the .alkyl phosphate is increased thereplacement of more than one group of the trialkyl phosphate isminimized. On the other hand. the increase of the relative quantity ofthe alkyl chlorosulfinate or the alkyl chloroiormate, favors thereplacement-of two, or in some cases, allthree of the .alkyl groups ofthe phosphate. Ordinarily the product which is obtained is'a mixture ofa phosphate in which only one alkyl or the other reactant. "triethylphosphate is -the most readily available of any of the trialkylphosphates; the use of triethyl phosphate as the starting material inprocesses in accordance with my invention is particularly contemplatedthereunder.

The temperature at which the reaction described is carried out-may varyconsiderably but I have found that ordinarily the masswill-be keptWithin the range of l-20-200 C. .over the major portion of the reaction.The temperature :em-

ployed also is .a factor in the time which will be used for the reactionto occur, although even at a high temperature cutting short the timewill limit the replacement of alk-yl .groups in the alkyl phosphateused. In some cases a time of 2 hours will be sufficient, while in othercases, up to 4 hours or =more will be desirable, while with the use ofhigh temperatures or where the degree of the replacement of-the alkylgroups is to be kept low, it may be that 1 hour would be sufficient. I

The reaction maybe carried-out in a reaction vessel equipped"withheating means and with means for agitating the mass. Also, provisionshould be made forthe escape of the ethyl chloride and the sulfurdioxide or the carbon dioxide which is formed in-the reaction. This ismost conveniently done by providing thechamber wtih a reflux condenserwhereby the gases referred to may escapewhereasthehigher boilingmaterials present in the mass willbe returned to the reaction chamber.

The following examples illustrate my invention:

Example 1.-There was placed in a reaction vessel fitted with anagitator, a water-cooled condenser and. a thermometer, 291 parts oftriethyl phosphate (1.6 mol), and-250 parts (1.6 mol) of.butyl-chlorosulfinate. The mass was well agitated and the temperaturewas slowly raised. When the temperature reached C. ethyl chloride andsulfur dioxide began to 'be evolved and was allowed to escape throughthe refiux co'ndenser. The temperature-was raised from 85 to C. over a 2-hour period and the mass was then maintained at 150 C. for 1; hourlonger. The loss in weight as the result of this reaction was 164 partsor 80% of theoretical.

When the reaction mixture obtained was flashdistilled at a pressure of1-2 mm., 27 parts of butyl chloride was collected in a Dry-Ice trap and321 parts of mixed phosphates was obtained. 29 parts of the mass waslost through the pump during this distillation, most of which was sulfurdioxide and butylene. The 321 parts of mixed esters was ,redistilledthrough a' spinningband has been replaced and a phosphate in which two5' of the alkyls have been replaced by the alkyl column at a refluxratio of 49 to l to give the following fractions:

148parts of triethyl phosphate 129 parts of diethyl butyl phosphate 43parts of dibutyl ethyl phosphate Phosphorus determinations showed16.53%, 14.38% and 12.70% in the respective fractions as compared totheoretical phosphorus contents of 17%, 14.76% and 13%. This correspondsto 39% conversion to diethyl butyl phosphate and 11.6% conversion todibutyl ethyl phosphate with a 62 utilization of the butyl group.

Example 2.-There was'placed in a reaction vessel as described in theprevious example a mixture of 214 parts (1 mol) of 2-ethylhexy1chlorosulfinate and 365 parts (2 mol) of triethyl phosphate. Thismixture was heated to 150 C. with good agitation over a 4-hour period.Ethyl chloride and sulfur dioxide began to be evolved through the refluxcondenser at 90 C. Loss in weight was 92.5 parts or 72% of theoretical.

483 parts of the reaction mixture was then distilled at 2-3 mm. pressurethrough a short-path still to give the following fractions:

62 parts in a Dry-Ice trap of a mixture of 2-ethyl hexene and 2-ethylhexyl chloride.

31 parts of 2-ethyl hexyl chloride at 30-40 C.

252 parts of triethyl phosphate at 56-60 C.

26 parts of a cut at 60-80 0., this cut being a mixture of triethylphosphate and diethyl 2-ethyl hexyl phosphate.

83.5 parts taken at 80-100 C. essentially consisting of diethy1 2-ethylhexyl phosphate.

The residue was 15.5 parts and the loss during distillation, most ofwhich was $02, was 23 parts.

The reaction as described herein may take place using any alkyl group upto carbon atoms. However, alkyl chlorosulfinates become less stable astheir molecular weight increases so that lower yields'are obtained withthe higher alkyl compounds. By my invention, however, phosphatescontaining any groups from methyl up through ethyl, propyl and butyl toalkyls of 10 carbon atoms may be prepared, the conditions for anycombination of alkyl groups being within the vjudgment of the individualoperator as adapted to the compounds being prepared.

Example 3.--182 parts of triethyl phosphate (1 mol) and 124.5 parts(.912 mol) of butyl chloroformate were mixed together and heated withgood agitation to 145 C. The temperature was then raised to 180 C. overa 4-hour period and the ethyl chloride and CO2 as well as the H01 andbutene formed were allowed to escape through a reflux condenser withwhich the reaction vessel was equipped. The reaction mass obtained wasfractionated in a spinning-band column and there was obtained 46.1 partsof diethyl-butyl phosphate, 20.3 parts of dibutyl ethyl phosphate, 111.1parts of triethyl phosphate and a residue of 19.5 parts. The yield onthe basis of the ethyl phosphate was 92% and on the basis of the butylgroup utilized was 43%.

The reactions which occur in the various processes Of my invention maybe illustrated by the following equations:

In these equations R and R may be any alkyls from 1 to 10 carbon atoms.As my invention is particularly adapted to the incorporation ofdifferent alkyl groups, it is preferable that the trialkyl phosphateused as the starting material be either triethyl or trimethyl phosphateand that the replacing alkyls be those of three or more carbon atoms.The products of my invention are useful for the preparation of variousphosphorus containing insecticide compositions or may, in some cases, beuseful for plasticizing purposes.

I claim:

1. A method for replacing, at least partially, the alkyl groups of atrialkyl phosphate the alkyl of which is of 1-10 carbon atoms whichcomprises reactin therewith at l20-200 C. a compound selected from thegroup of the alkyl chlorosulfinates and the alkyl chloroformates, thealkyl groups of which are of 1-10 carbon atoms and differ from those ofthe trialkyl phosphate, for a time sufficient to replace some of thealkyl groups of the trialkyl phosphate with alkyl groups from the otherreactant used.

2. A method of replacing alkyl groups from a trialkyl phosphate whichcomprises reacting at 120-200 C. the trialkyl phosphate the alkyl ofwhich is of 1-10 carbon atoms with an alkyl chlorosulfinate, having analkyl of 1-10 carbon atoms which difiers from that of the alkylphosphate whereby a mixed alkyl phosphate is obtained.

3. A method of replacing alkyl groups from a trialkyl phosphate whichcomprises reacting at 120-200" C. the trialkyl phosphate the alkyl ofwhich is of l-lO carbon atoms with an alkyl chloroformate, having analkyl of 1-10 carbon atoms which diiTers from that of the alkylphosphate whereby a mixed alkyl phosphate is obtained.

4. A method of preparing a mixed alkyl phosphate which comprisesreacting at 120-200 C. triethyl phosphate with an alkyl chlorosulfinate,the alkyls of which are of at least 3 and no more than 10 carbon atomswhereby some of the ethyl groups of the triethyl phosphate are replacedby higher alkyl groups.

5. A method of preparing a mixed alkyl phosphate which comprisesreacting at 120-200 C. triethyl phosphate with an alkyl chloroformate,th alkyls of which are of at least 3 and no more than 10 carbon atomswhereby some of the ethyl groups of the triethyl phosphate are replacedby higher alkyl groups.

6. A method of preparing a mixed ethyl butyl phosphate which comprisesreacting at 120-200 C. triethyl phosphate and butyl chlorosulfinatewhereby some of the ethyl groups of the triethyl phosphate are replacedby butyl groups.

7. A method of preparing an ethyl, 2-ethyl hexyl phosphate whichcomprises reacting triethyl phosphate with 2-ethy1 hexyl chlorosulfinateat l20-200 C., whereby some of the ethyl groups of the triethylphosphate are replaced by 2-ethyl hexyl groups.

8. A method of preparing ethyl butyl phosphate which comprises reactingtriethyl phosphate with butyl chloroformate at 120-200 C. whereby someof the ethyl groups of 1 the triethyl phosphate are replaced with butylgroups.

KENT C. BRANNOCK.

References Cited in thefile of this patent Rueggeberg et al., J. Am.Chem. Soc. (1948),

I vol. 70, pages 1802 to 1803.

Clark et al., J. Chem. Soc. (1950), pages 2023 to2030.

1. A METHOD FOR REPLACING, AT LEAST PARTIALLY, THE ALKYL GROUPS OF ATRIALKY PHOSPHATE THE ALKYL OF WHICH IS OF 1-10 CARBON ATOMS WHICHCOMPRISES REACTING THEREWITH AT 120-200* C. A COMPOUND SELECTED FROM THEGROUP OF THE ALKYL CHLOROSULFINATES AND THE ALKYL CHLOROFORMATES, THEALKYL GROUPS OF WHICH ARE OF 1-10 CARBON ATOMS AND DIFFER FORM THOSE OFTHE TRIALKYL PHOSPHATE, FOR A TIME SUFFICIENT TO REPLACE SOME OF THEALKYL GROUPS OF THE TRIALKYL PHOSPHATE WITH ALKYL GROUPS FROM THE OTHERREACTANT USED.